This invention relates to charging criteria used in a mobile telephone network for determining a price for a call between two subscribers.
In a fixed telephone network, a calling subscriber is aware of the charging criteria for the call already upon dialing the number of another, B subscriber as charging depends on whether it is a question of a local call, a long-distance call or an international call. In PBX exchanges (Private Branch Exchange) connected to a fixed telephone network, or in PABX networks, internal calls are free of charge. In cordless PBX's, part of the subscriber lines are replaced with a radio connection. In cordless PBX's, there are both fixed and cordless extensions. Cordless PBX's thus allow the users of cordless telephones mobility, which depends on the coverage area of cordless base stations. A coverage area typically covers the indoor premises of an office building.
In mobile telephone networks, which enable a high degree of mobility, the charging criteria used in a fixed network cannot be used as such owing to the structure and the mode of operation of the network. In the following, the structure and the operation of a mobile telephone network will be illustrated by means of a prior art GSM mobile telephone network shown in FIG. 1. Communication between a mobile station MS located within a cell, and the network takes place over the radio path via a base transceiver station (BTS). Base transceiver stations are connected to a base station controller (BSC), whose tasks include e.g. management of radio channels, as well as changeover procedures. One base station controller BSC thus controls a number of base stations BTS. The location of a mobile station is known with the accuracy of a so-called location area (LA) composed of a few cells. A mobile station may move within the location area without a need to update the location information related to it. A plurality of base station controllers are connected to one mobile services switching centre MSC, which performs the main switching functions of the mobile telephone network. The area of the cells controlled by the mobile services switching centre is termed as an MSC area, and all the calls originating or terminating within this area are switched via this MSC. Furthermore, the MSC connects the mobile telephone network to external networks.
The mobile telephone network also contains data bases of different kinds. In a Home Location Register (HLR), subscriber data is permanently stored regardless of the current location of the subscriber. The HLR contains the MSISDN number of the subscriber, the International Mobile Subscriber Identity code IMSI to be used inside the network, subscriber service data, and routing information on a Visitor Location Register VLR. The Visitor Location Register VLR is integrated to all present MSC's, and it is used for recording the subscriber data obtained from the HLR for the duration of the visit of the subscriber to the area of the VLR. The VLR contains the subscriber's IMSI, MSISDN, subscriber service data, and the location area identifier LAI that has been used by the subscriber for updating the location information. The location of the subscriber is thus known with the accuracy of a location area.
In the following, call establishment in a mobile telephone network will be disclosed for understanding the charging criteria: When a subscriber switches on his mobile station MS, e.g. in cell A (FIG. 1), it signals an updating request to a base station, which request is directed to a mobile services switching centre MSC1, and further to a visitor location register VLR. The request searches an IMSI from a home location register HLR. Thereafter, once it has been made sure in the signalling between the VLR and the mobile station that the IMSI is correct, the VLR sends an update request to the HLR, which will send the subscriber data to the VLR. Now the location of the subscriber is updated, i.e. the HLR knows the address of the VLR, and the VLR knows in which location area LAI the subscriber is located.
When a subscriber A calls a subscriber B located in a location area 22 of a second mobile services switching centre MSC2, he dials the MSISDN number of subscriber B into his mobile station. Signalling phases taking place after this are indicated with ringed numbers in FIG. 1, followed by the number to be switched in the phase in question. Indication MAP, TUP/ISUP represents the protocol to be used in the signalling in question. Next, mobile station MS-A sends base station 5 a message containing the dialed number, phase 1. When MSC1 receives the message, it analyses it and checks whether the request may be accepted. As a part of the check, the subscriber data of subscriber A is searched from the VLR of the MSC1, said data being recorded in connection of the above-mentioned location updating. If the request is accepted, MSC1 will send an interrogation message to the HLR, said message containing the MSISDN number of the mobile station of subscriber B, phase 2. On the basis of this number, the HLR searches the data on subscriber B, the data containing the address of the current VLR of subscriber B. Next the HLR asks the VLR to provide a roaming number by sending information IMSI to it, phase 3, "whereafter the VLR sends the roaming number MSRN to the HLR, phase 4. The roaming number MSRN is sent from the HLR to MSC1, phase 5. Thereafter, it is possible to route the call from MSC1 to MSC2 on the basis of the roaming number MSRN received from the VLR, phase 6. The mobile services switching centre MSC2 of subscriber B asks the VLR incorporated into it for the subscriber data on subscriber B. The subscriber data indicates the location area LAI of subscriber B, so that MSC2 is able to send a paging message via the base station controller 2 in question (phase 7) to cells f, g, and h in the location area. Once the mobile station MS-B of subscriber B has answered the paging, a call will be established to subscriber B. It must be noted that only after the mobile station of subscriber B has answered the paging message, mobile services switching centre MSC2 knows the location of subscriber 2 to the accuracy of one cell.
A Service Switching Point (SSP) of an Intelligent Network (IN) may also be connected to a mobile services switching centre. The physical architecture of an intelligent network is shown in FIG. 2. The service switching point SSP provides the user access to the network, and handles all the necessary switching functions. It is capable of detecting the service requests of the intelligent network. Functionally, the SSP comprises the call management and service switching functions. A Service Control Point (SCP) comprises service programs, which are used for producing services of the intelligent network. A Service Data Point (SDP) is a database comprising data of the subscriber and the network, which data is used by the service programs of the network for providing individual services. The SCP may use the services of the SDP directly or via a signalling network. An Intelligent Peripheral (IP) provides special functions, such as announcements, as well and audio and multi dialling detection. The Service Switching and Control Point (SSCP) consists of an SCP and an SSP in one node. The tasks of an Service Management Point (SMP) include database management, controlling and testing of the network, and collecting network information. It may be connected to all other physical entities. A Service Creation Environment Point (SCEP) is used for determining, developing and testing the intelligent network, as well as for feeding services to the SMP. An Adjunct (AD) of a service functionally corresponds to the Service Control Point SCP, but it is directly connected to the SSP. A Service Node SN may control the services of the intelligent network and carry out data transmission with the users. It communicates directly with one or more SSP's. A Service Management Access Point (SMAP) is a physical entity providing the users a connection to the SMP.
A Basic Call State Model (BCSM) determined in connection with the Intelligent Network describes different phases of call processing and contains points where call processing may be interrupted for starting a service of the Intelligent Network. It identifies the detection points in a call and connection process, in which the IN service logic entities may interact with basic call and connection management functions.
On account of an intelligent network it is possible to provide to the user of a fixed network and a mobile telephone network a large number of various services, such as a Private Numbering Plan (PNP), which enables the use of private numbers, and a Closed User Group, in which the users may call only the subscribers belonging to the same group. Furthermore, Private Branch Exchanges (PBX) may be connected to a mobile telephone network. A separate numbering block is determined for PBX subscribers in the numbering space of an MSC.
In a mobile telephone network in accordance with the prior art, all cells are equal as far as the price of a call is concerned. In mobile telephone networks, the price of a call is based on whether it is a question of a call between a mobile station and a fixed network, or a mobile-to-mobile call. Due to the mobility of mobile stations, the basic rule of charging is to charge a subscriber A for the connection between him and the home network of a subscriber B, and to charge subscriber B for the connection between his present location and his home network. This is considered fair, as, in accordance with call setup described above, neither the calling subscriber nor the first mobile services switching centre knows the location of subscriber B, i.e. in which cell the subscriber is located when the call setup is being started.
To increase the flexibility of the charging criteria, it is possible to set a special charging parameter, which will make it possible to apply a lower tariff to the calls made from the number related to the parameters during off-peak times, and correspondingly, a higher tariff than normally during the peak times. This parameter will make the charging criterion time-dependent, but, in other respects, the charging will follow the above-mentioned principles.
When the charging criterion of mobile telephone networks described above are compared with those of the fixed network, a few problems arise. Since all the cells are equal from the point of view of the mobile telephone network, no other charging criteria may be offered to different groups of users except for flexibility based on the time of the day. The distance between the calling and the called subscriber, or the location of the called subscriber cannot be taken into account in real time when determining the charging criteria. Special charging criteria are not available for certain intra-cell calls or for certain inter-cell calls.